Automatic burner control system for rotary kilns



W. E. LOHMAN Feb. 1, 1966 AUTOMATIC BURNER CONTROL SYSTEM FOR ROTARY KILNS Filed Feb. 18, 1964 llllllll INVENTOR. WILLIAM E. LOHMAN 2.). ELM M m d Ada-s ATTORNEYS United States Patet 3,232,592 AUTOMATIC BURNER CONTRQL SYSTEM FOR RGTARY KXLNS William E. Lehman, Black Eagle, Mont., assignor to The Anaconda Company, a corporation of Montana Filed Feb. 18, 1964, Ser. No. 345,782 4 Claims. (ill. 263- 39 This invention relates to rotary kiln drying apparatus and more particularly it relates to an automatic cyclical control system for a gas burner in such apparatus, and to a method of drying damp materials in rotary kilns equipped with the control system.

Rotary kilns are widely used for drying damp materials, and in this use the damp material is fed into the raised end of the canted rotary kiln and flows to discharge at the opposite lower end. A gas burner is generally posh tioned at the discharge end of the kiln and forces hot gases axially into the rotating kiln, thereby drying large quantities of damp material as it is continuously fed through the kiln. In spite of the extensive use of rotary kilns, no eifective operation of the kilns has been devised other than by constant attention of an experienced operator who is on the alelt for any change in the conditions of the kiln. Of the problems which an operator must detect, the most pressing is that of moisture control. Change in moisture content within the kiln is among the most difficult conditions to detect and ironically, is the one problem which must be recognized and corrected early, for if it goes undetected for even a short period of time many other problems ensue. The presence of excessive moisture in the kiln almost immediately causes formation of rings of material on the inner walls of the kiln which in turn seriously impede the flow of material through the kiln, shorten brick life, and result in excessive gas consumption.

The casual relationship which excessive moisture content and the resulting ring function bears to the subsequently arising problems is obvious. Once the rings are formed, wet material tends to build up at the feed end of the kiln thereby requiring greater amounts of gas to achieve the desired drying effect, while less material is being fed through the kiln because of the impeditive ring formations. It is clear then that the formation of rings must be prevented or removed immediately after their formation or suffer the consequences flowing from their presence. In practice, ring formations are invariably found in rotary kilns because the operator, regardless how experienced or alert, cannot give constant attention to a single kiln, as he is generally responsible for the operation of several kilns and special attention to any one is not practical.

It is an object of this invention to provide an automatic cyclical control system for use with the gas burner or" a rotary kiln whereby the air-to-gas mixture will be varied at predetermined intervals so that the flame will sweep substantially the full length of the kiln and become concentrated at the feed end of the kiln and thereby either remove any ring formations or substantially reduce the moisture content at the feed end of the kiln so as to preclude ring formation. 1 have particularly found that by automatically controlling the air-to-gas mixture of the gas burner of a rotary kiln so that it will cyclically cause the flame to sweep the length of the kiln, not only is the kiln maintained substantially free from ring formation but it has also resulted in a more substantial saving in gas consumption than has heretofore been realized. Thus, the new control system not only solves the problem which faced the art but gives the additional surprising advantage of substantial savings in operation expenses. Broadly stated, the automatic control system is to be used in rotary kiln drying apparatus of the type having a gas dryer burner, and it is comprised of a shutter for controlling the air intake of the burner which is mounted to move relative to the burner body, reciprocating means connected to the shutter for effecting movement of the shutter to fixed positions relative to the burner body to vary the airto-gas mixture, and timer means operatively connected to the reciprocating means for periodic actuation of the reciprocating means whereby the flame will sweep through the kiln at predetermined intervals.

The invention also provides an apparatus for controlling moisture content in the kiln and removing ring forma tions at the feed end of the kiln for use with the process of drying materials in a rotary kiln which comprises apparatus for cyclically increasing and decreasing the amount of air in the air-to-gas mixture of a gas burner located at the discharge end of the kiln to cause the flame to be concentrated alternately at the feed end and discharge end respectively of the kiln.

With the apparatus of the invention, the operator empirically determines the time it takes for the moisture content to reach the level at which ring formations begin to form for the particular slurry being dried, and once the timer is set according to these values it has been found that substantially all ring formations and the related difiiculties are eliminated, andthe rotary kiln can be operated with greater efiiciency and less attention than heretofore thought possible. Also, as indicated above, because the conditions remain stable, the gas consumption has been found to be far less for a given quantity of slurry than that consumed with methods and apparatus presently in use.

A preferred embodiment of the invention is described hereinbelow with reference to the drawings wherein:

FIG. 1 is a side elevation of a rotary kiln employing the automatic burner control of the invention; and

FIG. 2 is a side elevation of the burner control apparatus of the invention partly in schematic and partly in section.

A rotary kiln 10 shown in FIG. 1 consists of a steel cylinder 11 which is inclined slightly from the horizontal and is rotatable about its axis. Rotation is accomplished by a girth gear 12 which is mounted about the cylinder 11 substantially at its midpoint and a drive gear 13 which is attached to a motor 14. The cylinder 11 is supported on flanged girth rings 15 and 16 which are attached to the cylinder 11 along its respective end portions. Each of the girth rings 15 and 16 respectively is mounted on rollers 17 and 18 respectively which ride in the flange rings and aid greatly in rotation of the cylinder. Extending into the inlet end 24) of the kiln is a feed tube 21 and mounted to the outlet end 22 of the kiln is a discharge hood 23. A burner 24 is rotated at the outlet end of the kiln with its nozzle 25 extending through the discharge hood into the kiln itself. The burnor body 26 which is attached to the nozzle 25 flares outwardly to a larger diameter as it emerges out of the hood 23. Extending axially into the burner body 26 is an inlet gas tube 27. Mounted along one portion of the gas tube 27 along that portion which is located at the flared end of the hood 26 is a key 29. Slidably mounted on the gas tube 27 and containing a keyway into which the key 29 is insertable in an externally threaded sleeve 3t. Threaded on the sleeve 30 is a substantially circular plate 31 which has a diameter slightly larger than the diameter to which the end of the burner body flares. Connected to the end of the sleeve 3% remote from the burner body 26 is a bracket 31 which is attached to a rod 32 and in turn is connected to piston of a double acting air cylinder 33. The air cylinder 33 is shown also mounted on the gas inlet tube 27 by means of brackets 34 and 34 which are journalled on the inlet tube. Leading from opposite ends of the air cylinder 33 are air tubes 35 and 35' which are connected to a four-way solenoid valve 36 through which compressed air is fed from a suitable source through tube 37. Connected to the solenoid valve 36 is a timer assembly 38, and variable speed control valve 39. A manual control valve 49 and a regulator gauge assembly 41 are positioned between the air source and the solenoid valve 36.

In operation, the shutter plate 31 is adjusted in its relation to the burner body 26 by rotating it along the threaded sleeve 33 so as to obtain the correct air-shutter opening 42 therebetween. Since the rod 32 of the air cylinder 33 is shown in its most extended position the air-shutter opening 42 is one which permits a minimum amount of air in the air-to-gas mixture of the burner and thereby causes the fiame to sweep the full extent of the rotary kiln ,so as to impinge upon the walls of the kiln at the inlet end thereof for the removal of any ring formations. The timer 38 is adjusted to maintain the shutter plate 31 in the position shown a predetermined length of time so that ettective removal of any ring formations can be realized. Once this predetermined length of time has lapsed, the solenoid valve is actuated causing the cylinder 33 to retract the rod 32 and withdraw the shutter plate 31 away from the burner body 26 by sliding the sleeve 30 along the gas inlet tube 27 to the position shown in dotted lines. In its withdrawn position the air-shutter opening 42 is increased substantially so that more air is allowed in the air-to-gas mixture thereby withdrawing the flame from its concentration at the inlet end of the kiln and causing the hot gases to impinge farther down toward the outlet end of the kiln in its normal operating position. The timer 38 controls the length of time which the shutter plate 31 is held within it withdrawn on normal position and after its time has lapsed it will once again be moved to its position adjacent the burner body as shown, and such opening and closing of the shutter plate will be cyclically effected throughout the drying operation.

Of course the flame can be caused to sweep to the end 7 of the kiln by controlling the gas source, but increasing the amount of gas fed to the burner to cause the sweeping flame results in a prohibitive excess of gas consumption,

and the same effect is realized according to the invention by changing the air intake in a typical inspirating gas burner.

I claim:

1. In a rotary kiln drying apparatus of the type having a gas dryer burner consisting of a burner body having one end extending into the rotary kiln and an air inlet end portion opening out of the rotary kiln for intake of air for mixture with gas fed into the burner body through a gas inlet tube, the improvement in an automatic control system in combination therewith comprising:

(a) a shutter mounted to move relative to the air inlet of the burner body for controlling the air intake of the burner,

(b) reciprocating means connected to said shutter for efiecting movement of the shutter to fixed positions relative to the air inlet of the burner body to vary the air-to-gas mixture therein, and

(c) timer means operatively connected to said reciprocating means for periodic actuation of the reciprocating means whereby the flame will sweep through the kiln at predetermined intervals.

2. In a rotary kiln drying apparatus of the type having a gas dryer burner consisting of a burner body having one end extending into the rotary kiln and an air inlet end portion opening out of the rotary kiln for intake of air for mixture with gas fed into the burner body through a gas inlet tube, the improvement in an automatic control system in combination therewith comprising:

(a) a shutter plate mounted adjacent to the air inlet of the burner body and defining with said body an air-shutter opening through which air is taken for mixture with gas, said plate mounted to move relative to the air inlet of the burner body for controlling the air intake of the burner,

(b) reciprocating means connected to said shutter plate for eiiecting movement of the shutter plate to fixed positions relative to the air inlet of the burner body to vary the air-shutter opening to change the air-togas mixture, and

(c) timer means operatively connected to said reciprocating means for periodic actuation of the reciprocating means whereby the flame will sweep through the kiln at predetermined intervals.

3. In a rotary kiln drying apparatus of the type having a gas dryer burner consisting of a burner body having one end extending into the rotary kiln and an air inlet end portion opening out of the rotary kiln for intake of air for mixture with gas fed into the burner body through a gas inlet tube, the improvement in an automatic control system in combination therewith comprising:

(a) a shutter plate adjustably mounted adjacent to the air inlet of the burner body and defining with said body an air-shutter opening through which air is taken into the burner for mixture with gas, said plate mounted to move relative to the air inlet of the burner body for controlling the air intake of the burner,

(b) a slid-cable support for said shutter plate which is adjustably movable toward and away from said air inlet of the burner body,

(c) reciprocating means attached to said support for sliding the support and the shutter plate relative to the burner body between predetermined positions relative to the burner body to change the air-to-gas mixture, and

(d) a timer connected to the reciprocating means for periodic actuation of the reciprocating means where by the flame will sweep through the kiln at predetermined intervals.

4. In a rotary kiln drying apparatus of the type having a gas dryer burner consisting of a burner body having one end extending into the rotary kiln and an air inlet end portion opening out of the rotary kiln for intake of air for mixture with gas fed into the burner body through a gas inlet tube, the improvement in an automatic control system in combination therewith comprising:

(a) a shutter plate adjustably mounted adjacent to the air inlet of the burner and defining with said body an air-shutter opening through which air is taken into the burner for mixture with the gas, said plate mounted to move relative to the air inlet of the burner body for controlling the air intake of the burner, said plate mounted to move relative to the burner body for controllhig the air intake of the burner,

(b) a sleeve member slidably positioned on a gas inlet pipe, said shutter plate mounted on said sleeve member,

5 6 (c) an air cylinder attached to said sleeve member for References Cited by the Examiner reciprocating it and said shutter plate relative to the UNITED STATES PATENTS air inlet of the burner body between predetermined t t h thn t t 2,240,485 5/1941 Arrnel 263-53 8 ange oigas 2,298,257 10/1942 Reaser et a1. 263-53 X ((1) an air valve for controlling the air feed into the 5 cylinder, and FOREIGN PATENTS (e) a timer connected to said valve for periodic actua- 196,404 3/1908 Germany.

tion of the reciprocating means whereby the flame will sweep through the kiln at predetermined inter- WILLIAM O D Actmg Prlmary Exammer' vals. 10 JOHN J. CAMBY, Examiner. 

1. IN A ROTARY KILN DRYING APPARATUS OF THE TYPE HAVING A GAS DRYER BURNER CONSISTING OF A BURNER BODY HAVING ONE END EXTENDING INTO THE ROTATY KILN AND AN AIR INLET END PORTION OPENING OUT OF THE ROTARY KILN FOR INTAKE OF AIR FOR MIXTURE WITH GAS FED INTO THE BURNER BODY THROUGH A GAS INLET TUBE, THE IMPROVEMENT IN AN AUTOMATIC CONTROL SYSTEM IN COMBINATION THEREWITH COMPRISING: (A) A SHUTTER MOUNTED TO MOVE RELATIVE TO THE AIR INLET OF THE BURNER BODY FOR CONTROLLING THE AIR INTAKE OF THE BURNER, 